North Korea and the US vowed to work to end Pyongyang's weapons programmes at a landmark June summit in Singapore, but have struggled to reach an agreement to accomplish that goal.
It was important to maintain diplomatic and economic pressure, Pompeo said, adding the United States took very seriously any relaxation of UN sanctions against North Korea.
Over 10,000 new North Korean workers have registered in Russia since September in potential violation of UN sanctions to pressure Pyongyang to give up its nuclear weapons.
US Director of National Intelligence Dan Coats also said that denuclearisation was a complex process.
There has been no sign of concrete action toward denuclearisation by Pyongyang since US President Donald Trump and North Korean leader Kim Jong Un held a summit in Singapore on June 12.
The allies also expressed concern about Iran's intensified missile tests and said the alliance was committed "to permanently ensuring that Iran’s nuclear programme remains peaceful".
Trump said China "may be exerting negative pressure" in reaction to punitive US tariffs on Chinese goods.
Pompeo said that North Korea, in the “many hours of talks’’ at a walled-off guesthouse outside downtown Pyongyang, reiterated its commitment to denuclearization.
The White House has characterized ongoing meetings as positive but not commented on recent news reports of US intelligence assessments saying North Korea has been expanding its weapons capabilities.
White House national security adviser John Bolton said Secretary of State Mike Pompeo will likely discuss that proposal with the North Koreans soon.
Moon's comment was made in a letter sent to commemorate the opening ceremony of the United Nations Command and US Forces Korea's new headquarters building at US Army Garrison Humphreys south of Seoul.
Pompeo said he would be leading the ongoing talks with Pyongyang, but declined to discuss details. 'They're watching this hearing,' he said.
Speaking to CNN in a telephone interview conducted on Sunday and reported by the network on Monday, Pompeo said he wanted to see continued progress towards North Korean denuclearization
The US-based North Korea monitoring group 38 North said in an analysis at the end of last week there had been no sign of any activity toward dismantling of any missile test site.
The North Korean leader also promised during a meeting with Xi in Beijing to cooperate with Chinese officials to secure "true peace" in the process of "opening a new future" on the Korean peninsula.
China on Tuesday praised the summit between US President Donald Trump and North Korean leader Kim Jong Un as historic and called for "full denuclearisation" to resolve tensions on the Korean peninsula.
So far neither Trump nor Kim have changed their collegial tone with regard to the other, suggesting both are open to suggestions.
Philippine President Rodrigo Duterte's opinion of North Korean leader Kim Jong-un has changed from one of derision to one of admiration.
Israel is concerned Russia might provide Syria with the S-300 surface-to-air missile system, which analysts say would improve Russia's ability to control air space there.
The British government hopes the plan also indicates an effort to negotiate in good faith.
For Kim Jong Un, fully giving up nuclear weapons would mean a dramatic reversal for an authoritarian leader who has not only staked his security on his nuclear arsenal, but also spent years publicly celebrating such weapons as an integral part of his regime’s legitimacy and power.
Kim Jong-un has visited Pyongyang's ally Beijing for the first time, ahead of proposed summits with Seoul and Washington.
A meeting in Finland between North Korea, South Korea, and the United States will not involve denuclearisation.
South Korea’s Chung Eui-yong, the US' H. R. McMaster, and Japan’s Shotaro Yachi met to discuss North Korea and the denuclearisation of the Korean peninsula.